Scan Disk card not recognized?

Scan Disk card not recognized?

I can't get my Note3 to recognize an SD card. I've done youtube videos and pretty sure I've got it installed right. I tried with a ScanDisk 8gb card from my old phone, and also with a brand new ScanDisk 64gb card purchased from Best Buy. The card fits in nicely, but the phone doesn't seem to recognize the card. Under Settings/General/Storage, the option to "Mount SC card" at the bottom is greyed out. There's no other setup I need to do, is there?
Loving this phone.